The present invention relates to systems and methods for performing measurements of eye aberrations, such as prior to laser surgery, and, more particularly, to such systems and methods for deinterlacing video camera images.
Video signals are known to be represented using a pair of fields, with a first field comprising, for example, odd-numbered horizontal lines, and a second field comprising even-numbered horizontal lines. In the interlaced scan format, each field of image data is scanned twice, once for each field, with the pair of fields then constituting one frame.
In the non-interlaced or progressive-scan format, an image is represented in its entirety using only a single field that includes pixels in all horizontal lines of the field matrix. This results in a higher-quality image reproduction, because of a lack of visual artifacts compared with interlaced scan displays. As a result, it is desirable to develop systems and methods for deinterlacing interlaced video image data.
The measurement of eye aberrations using a progressive-scan video camera is known in the art, which is more expensive than a camera using an interlaced scan format.
In the field of video image processing, Ishikawa (U.S. Pat. No. 4,768,092) uses interlaced image signals to create a high-resolution image by interpolating between two interlaced images. Lang (U.S. Pat. No. 4,845,557) manipulates one of two interlaced fields to detect and suppress motion. Motion detection is also taught in Hara (U.S. Pat. No. 5,047,849), with the use of multiple frames. Fast movement is also compensated for in Edgar (U.S. Pat. No. 5,191,413) by deleting an image area that is determined to have moved from an adjacent image area.
Motion artifacts are reduced by Knee (U.S. Pat. No. 5,504,531) using interpolation. Deinterlacing is accomplished by Sezan et al. (U.S. Pat. No. 5,521,644) with the use of four consecutive fields. Young et al. (U.S. Pat. No. 5,929,935) alter intensities of pixels to reduce image flicker.
It is therefore an object of the present invention to provide a system and method for deinterlacing eye images for assisting in performing ocular measurements.
It is a further object to provide such a system and method that obviates the need for using expensive progressive-scan cameras.
It is an additional object to provide such a system and method that compensates for the motion of an entire image relative to a camera.
It is another object to provide a system and method that removes motion artifacts in video scans.
These and other objects are achieved by the present invention, a video image deinterlacing system and associated methods. The composite video image to be deinterlaced by the present invention comprises alternating even and odd rows of pixels, each pixel having an intensity value associated therewith. The even rows comprise a first image, and the odd rows comprise a second image. The first and the second images are recorded at different times, thereby introducing a possibility of motion artifact between the collection of the first and the second images.
The method comprises the step of receiving a composite image and computing a first average horizontal intensity difference between the first image and the second image. Next the first image is offset by one pixel in a first horizontal direction to form a first horizontally offset image and a second average horizontal intensity difference is computed between the first horizontally offset image and the second image.
The first image is then offset by one pixel in a second horizontal direction that is opposite the first horizontal direction to form a second horizontally offset image. A third average horizontal intensity difference is computed between the second horizontally offset image and the second image, and a minimum average intensity difference is determined from a comparison of the first, the second, and the third average horizontal intensity differences.
The first image is then shifted in a horizontal direction determined to achieve the minimum average horizontal intensity difference, and the horizontally shifted first image is combined with the second image to form an improved composite image.
A system is also provided as part of the present invention for performing the above-described method.
The features that characterize the invention, both as to organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description used in conjunction with the accompanying drawing. It is to be expressly understood that the drawing is for the purpose of illustration and description and is not intended as a definition of the limits of the invention. These and other objects attained, and advantages offered, by the present invention will become more fully apparent as the description that now follows is read in conjunction with the accompanying drawing.